This invention relates to a new method for treatment of osteoporosis and bone mineral disorders and to prevent bone loss, fractures and other abnormal clotting patterns, urogenital discomfort, prevention and treatment of cardiovascular diseases, and other conditions associated with the reduction in ovarian function in middle-aged women, with a nitric oxide synthase substrate (L-arginine), a nitric oxide donor, or both, alone or in combination with an estrogen and/or a progestin. Same compounds are also useful in men to decrease bone turnover and hence prevention and treatment of osteoporosis and for treatment of other metabolic bone disorders.
It is now well known, that hormone replacement therapy, such as estrogen treatment, improves or reverses the adverse effects of the cessation of sex steroid secretion by the ovaries during menopause. Estrogens have also been shown to prevent bone loss and improve a variety of functions including mood and psychological well-being in postmenopausal women. Estrogens have been shown to effect arterial tone and this may help to explain the reduction in hot flushes and decrease the cardiovascular mobility and mortality in postmenopausal women with estrogen replacement therapy. Unopposed estrogen therapy in postmenopausal women has been associated with endometrial hyperplasia and endometrial cancer.
Many studies have shown that the addition of progesterone to estrogen replacement therapy decreases the risk of endometrial cancer and even reverses endometrial hyperplasia. However, progestins are not without untoward side effects. Progestins may oppose the beneficial effects of estrogens on the cardiovascular system by inducing an adverse lipid profile in circulation. Progesterone may also counteract the beneficial effects of estrogen on vascular walls. Moreover, irregular or withdrawal bleedings are common with combined estrogen-progestin therapy. The current hormone replacement therapy (HRT) employs combinations of estrogen and progestins as in the case of most contraceptives.
One of the most exciting recent advances in biology and medicine is the discovery that nitric oxide which is produced by endothelial cells (as one of the endothelial derived relaxing factors) and that it is involved in the regulation of vascular tone, platelet aggregation, neurotransmission and immune activation in a favorable fashion (Furchgott and Zawaszki, 1980; Moncada, Palmer and Higgs, 1991; Ignarro, 1991). Nitric oxide is an important mediator of relaxation of the vascular smooth muscle (Moncada, Palmer and Higgs, 1991), was formerly known as EDRF (endothelin-derived relaxing factor) (Furchgott and Zawaszki, 1980; Moncada, Palmer and Higgs, 1991). Nitric oxide is synthesized by the oxidative deamination of a guanidino nitrogen of L-arginine by at least different isoforms of a flavin-containing enzyme, nitric oxide synthase (Moncada, Palmer and Higgs, 1991). Synthesis of nitric oxide has been shown to be competitively inhibited by analogues of L-arginine; N.sup.G -nitro-L-arginine methyl ester (L-NAME), N.sup.G -monoethyl-L-arginine (LMMA), N-iminoethyl-L-arnithine (L-NIO), L-monomethyl-L-arginine (L-NNMA) and L-N.sup.G -methylarginine (LNMA) and Nw-nitro-L-arginine (L-NA).
Nitric oxide elevates levels of cGMP (1, 3, 5-cyclic guanosine monophosphate) within the vascular smooth muscle to produce relaxation and to reduce blood vessels tone (Moncada, Palmer and Higgs, 1991). Nitric oxide is also produced by macrophages and other immune cells. Nitric oxide binds to heme molecules and activates soluble guanylate cyclase (Ignarro, 1991) to increase the intracellular content of cGMP. It has long been recognized that nitrovasodilators, such as nitroprusside and nitroglycerine, inhibit vascular smooth muscle contractility to produce relaxation or to reduce vascular tone. These agents have been used since the late 1800's as vasodilators. However, only recently has the mechanism of action of these compounds been realized. Nitrovasodilators are now classified as nitric oxide donors because they are metabolized at the sites of interests to release nitric oxide (Moncada, Palmer and Higgs, 1991). The long-term use of nitrovasodilators may be regarded as substitution or a replacement therapy for a failing physiological mechanism.
There is a substantial body of evidence from animal studies that a deficiency in nitric oxide contributes to the pathogenesis of several diseases including hypertension, atherosclerosis and diabetes (Moncada, Palmer and Higgs, 1991) and toxemia of pregnancy (Yallampalli et al., 1993). There are many recent studies showing that the inhibition of nitric oxide synthase dramatically increases blood pressure. For example, the inhibition of nitric oxide synthesis with L-NNMA, L-NA or L-NAME leads to elevation of blood pressure and suggests that reduction of NO may contribute to the pathogenesis of hypertension (Moncada and Palmer, 1992). Furthermore, L-NAME-treatment potentiates the presser responses to angiotension, blunting of the release of nitric oxide by umbilical vessels (Pinto et al., 1991). The physiological decrease in blood pressure in pregnant spontaneous hypertensive rats was also shown to depend on endothelial derived nitric oxide (Ahokas, Merces and Sibal, 1991). Additionally, infusion of L-NA increases blood-pressure in pregnant rats and potentiates responses to vasopressors (Molnar and Hertelendy, 1992). These studies suggest that impaired nitric oxide synthesis may be an important mechanism in the etiology of several cardiovascular dysfunctions.
Nitric oxide synthesis and nitric oxide effector system (cGMP-dependent relaxation mechanism) are thought to be regulated by steroid hormones. There is an increase in cardiovascular diseases in women following menopause and these might be related to the decrease in sex steroids and thereby an alteration in nitric oxide. Female steroid hormones have been shown to modulate endothelium-dependent relaxation of vascular smooth muscle via nitric oxide. Estradiol treatment of rats causes increased nitric oxide production by vascular tissues, whereas progesterone counteracts this phenomenon (Miller and Van Houtte, 1991). It is well known that pregnancy is associated with an increase in cardiac output and a decrease in the resistance of virtually all the vascular beds in the body, although the mechanism of this phenomenon is not known. It is possible that this may be associated with changes in nitric oxide production or effects as a result of elevated steroid hormone levels. One important observation with regard to the above mechanism is that antiprogestins elevate blood pressure in animals and they produce hot flushes in humans, both males and females. The hot flushes may be mediated by the inadequate steroid action on the release of nitric oxide. Hot flushes are a primary symptom in menopausal, postmenopausal women and they are relieved by both estrogen and progesterone.
Studies described herein (see below) show that nitric oxide and the subsequent relaxation of the uterus is controlled by progesterone. The relaxation effects of the nitric oxide substrate, L-arginine, are greater in late pregnancy when progesterone levels are elevated in pregnant rats. Also there is greater uterine relaxation with L-arginine when uterine strips are taken from nonpregnant, ovariectomized rats treated with progesterone. In addition, treatment with pregnant rats with the nitric oxide inhibitor produces signs and symptoms of preeclampsia (e.g. hypertension, fetal retardation and proteinurea--the classical triad of preeclampsia). These symptoms are related to the decrease in vascular resistance and placental perfusion. Preeclampsia is also a well known model of accelerated atherosclerosis, as the decrease in placental perfusion is accompanied by increased fibrin deposition in placental vessels and increased thrombus formation.
EP 0441 119 A2 mentions the use of L-arginine in the treatment of hypertension and other vascular disorders. It suggests that the mechanism by which L-arginine is effective for this purpose is because it may be the physiological precursor of "the most powerful endothelial-derived releasing factor, nitric oxide". The use of L-arginine in combination with other pharmaceutically active agents is not discussed in EP 0441 119 A2 publication.
This invention is also applicable to both primary and secondary osteoporosis in both females and males. In the female, the method of choice of treatment of primary osteoporosis is estrogen replacement therapy and in the case of male, the method of choice of treatment of primary osteoporosis is androgen replacement therapy. In both sexes for the secondary osteoporosis the underlying causative factors are numerous, including medication-induced osteoporosis (e.g.,corticosteroids, antiepileptics, anticoagulants, thyroxine), immunosuppressant agents used in prevention of graft rejection and other disorders (cyclosporin), malignancies (e.g., multiple myeloma), immobilization-induced bone loss and other conditions of bone loss.
One aspect of the present invention provides a method for the prevention and treatment of primary and secondary osteoporosis, including medication induced-osteoporosis (i.e. corticosteroid-induced osteoporosis) and other metabolic bone disorders with a nitric oxide substrate and/or donor.
It is another object to provide such a method in which a progestational agent is used in combination with a nitric oxide substrate and/or donor for the prevention and treatment of osteoporosis and other metabolic bone disorders.
It is a further object to provide a method for the prevention and treatment of osteoporosis and other metabolic bone disorders using an estrogenic agent in combination with a nitric oxide substrate and/or donor.
It is another object to provide a method for prevention and treatment of osteoporosis and other metabolic bone disorders using a combination of an estrogenic agent and progestational agent with a nitric oxide substrate and/or donor.
Another object is to provide a method of prevention and treatment of male primary and secondary osteoporosis and other metabolic bone disorders using nitric oxide substrate and/or donor.
A further object is the provision of pharmaceutical compositions useful in practicing the methods of this invention.
Other objects will be apparent to those skilled in the art to which this invention pertains. Another object is to provide a method of prevention and treatment of male primary and secondary osteoporosis and other metabolic bone disorders using nitric oxide substrate and/or donor.